1. Field of the Invention
The invention relates to pistons for combustion engines consisting of an upper part forming the piston crown and a lower part forming the piston body, the upper part and lower part abutting each other in the direction of the piston axis via annular contact surfaces and being connectable together by means of a coupling element such as a gudgeon pin or a gudgeon pin bushing.
2. Description of the Prior Art
Such multi-part pistons are known. In such pistons, the upper and lower parts, which can be manufactured from differing materials or from the same material, must be connected together by coupling elements, such as, for example screws, or in the known so-called articulated pistons with pendulum shaft by the gudgeon pin which engages through both piston components.
The known multi-part screwed pistons consists in most cases of two differing materials, the material of the upper part consisting for example of steel or cast iron owing to its high thermal and mechanical loading, whilst the lower part, which has basically a guidance function, can consist of weight-saving light metal. Screwed multi-part pistons have the disadvantage that as a result of the screwed connection their weight is increased and assembly is made more difficult so that it is impossible to manufacture such pistons economically. Moreover, screwed connections are often problematical when subjected to cyclic thermal and mechanical loading.
In the known articulated pistons, in which both the upper part of the lower part can consist of the same or of differing materials, the ignition force is transferred from the upper part via the pin directly to the connecting rod whilst the lateral guidance forces are absorbed by the "pendulating" lower part, i.e. the lower part which is not supported in the axial direction on the periphery of the piston upper part (e.g. DE-PS No. 571 548, DE-AS No. 22 53 961, DE-OS No. 27 17 692 and DE-OS No. 33 38 419 as well as DE-PS No. 2 717 084).
The disadvantage of the known articulated piston lies in the fact that the upper part, which is not supported by the lower part in the vicinity of the outer diameter, is strongly deformed by the large ignition forces exerted particularly on the periphery of the piston end surface. In order to resist these loadings, the upper part must be rigid, i.e. provided with thick walls or with ribs, which causes an increase in weight. Moreover, the provision of cooling channels, is not possible without considerable expense owing to the peripheral gap between the upper and lower parts (see in particular DE-OS No. 33 38 419).